1. Field of the Invention
The present invention relates to a control unit for a generator driven by an engine being provided with a plurality of cylinders, and particularly to a control unit for a generator driven by such an engine in which a certain number of cylinders to be operated is suitably selected in accordance with the current operating conditions.
2. Description of the Prior Art
A conventional control unit of the type mentioned above has been constructed as illustrated in FIG. 1 in which an AC generator is driven by a so-called cylinder number variable engine mounted on a vehicle (not shown) and in which a suitable number of cylinders to be ignited for reducing fuel consumption is selected in accordance with its load. The AC generator comprises armatkure coils 101 connected to each other in three-phase star manner and a field coil 102 being related magnetically to the armature coils 101 and in which current supplied to the field coil 102 is controlled as described hereinbelow. The coils 101 are bridge-connected by means of diodes of a full-wave rectifier 2 to supply DC output. First and second rectification output ends 201 and 202 of the rectifier at each of which cathodes of the diodes in each phase are commonly connected to one another are connected with a positive terminal of a battery 4 and a control input terminal of a voltage regulator 3, respectively, whilst a third rectification output end 203 of the rectifier at which anodes of the diodes are commonly connected is connected with its vehicle chassis, i.e., ground.
The voltage regulator 3 includes resistances 307 and 308 connected in series between the control input terminal and ground for dividing voltage applied from the output terminal 202; a transistor 305 to the base of which the voltage divided is inputted through a Zener diode 306 and the collector of which is connected to the control input end through resistances 304 and 309; and a transistor 303, the base of which is connected to the collector of the transistor 305, being Darlington-connected with a transistor 302. Collectors of the transistors 302 and 303 provide a control output end to be connected with the coil 102 and these collectors are connected to the control input end through a diode 301. A connection point between the resistances 304 and 309 is connected to the positive terminal of the battery 4 and to the output end 202 through a charge display lamp 6 and a diode 7.
In operations of the conventional control unit as described above, when a switch 5 is closed in relation to starting of the engine, a current is supplied from the battery 4 to the base of the transistor 303 through the switch 5, the diode 310 and the resistance 304 so that the transistors 302 and 303 are turned ON to ground an end of the coil 102 therethrough. Thus, the field current is supplied from the battery 4 through the switch 5, the lamp 6, the diode 7, the output end 202, and the coil 102 to turn of the lamp 6. When the engine starts the rotation thereof, the coil 101 induces AC output corresponding to speed of revolution of the engine as well as field current of the coil 102 to supply the resulting AC to the rectifier 2. When the voltage from the output end 202 of the rectifier 2 rises to reach a value higher than the voltage of the battery 4, the diode 7 is reversely biased so that the current passing through the lamp 6 is interrupted to turn off the lamp. Furthermore, when the output voltage rises, the Zener diode 306 is turned ON so that the transistor 305 is turned ON, whereby the transistors 302 and 303 are succeedingly turned OFF. As the result, the field current of the coil 102 is interrupted to lower the AC output of the coil 101. When the AC output lowers, the transistors 302 and 303 again turn ON so that the above-mentioned operations are repeated. Thus, the output of the generator 1 is regulated, whereby charging current of the battery 4 is adjusted to an optimum value.
However, such engine for driving the generator as described above is liable to become unstable in respect of the rotation thereof, for instance, the engine generates abnormal vibration and the like undesirable phenomena due to fluctuation of load, because the torque generated is small in the case where the engine is driven by a decreased number of the cylinders thereof, more specifically, where the engine is in its idling mode. Therefore, it is desirable that such generator is controlled as a load of the engine in such a manner that its required driving torque corresponds to the rotation of the engine.